Does anyone know if there is an actual standard bolt size for DSA Para lowers? I’m trying to install a Lucky Irishman ACR stock adapter and the bolt is way too tight. It also bottoms out before seating all the way. Is there a different size for the aluminum lowers?

There are two main sizes.  One is for steel trigger housings originally made for fixed-stock rifles.  The other is for trigger housings using the thread size used on hiduminium fixed-stock trigger housings, which also was used by FN as the standard size for paras in general (these bolts are wider; some were steel, and some hiduminium).  DSA uses the former.  Both are the same length.  As far as factory parts go, there were never short ones made like that.